/Engine/Plugins/2D/Paper2D/Source/Paper2D/Public/AlphaBitmap.h
Flushes values smaller or equal to LowAlphaThreshold to 0, and values greater or equal to HighAlphaThreshold to 255.
void ThresholdImageBothWays ( int32 LowAlphaThreshold, int32 HighAlphaThreshold )